Presently, a method of displaying a bar code with black and white bars in various densities, and reading with an optical code reader such as bar code reader or a laser, is widely used in the distribution industry, production control, and other fields.
The bar code has limited information transmission capacity because only black and white bars are displayed at narrow or wide intervals in a one-dimensional direction. For example, Chinese characters, Japanese hiragana, and Arabic letters cannot be expressed.
Accordingly, the present inventor previously proposed two-dimensional code symbol marks in a matrix, and the apparatus and method of reading them in the Japanese Laid-Open Patent No. Sho. 64-86289, Japanese Laid-Open Patent No. Sho. 64-76176, and PCT/JP90/00980.
The two-dimensional symbol mark is effective because an extremely large amount of information can be displayed and transmitted, and this two-dimensional code symbol mark may be read by an image reader and the image is processed.
Since the code symbol is read in very fine intervals, for example, 0.1 mm by the image reader and processed by an analog process, the quantity of data to be read is very large and the memory capacity required is larger, it takes time to read, and also decoding of the code symbol mark is time-consuming.